On 12/01/2016 09:12 PM, David Gibson wrote:
On Wed, Nov 30, 2016 at 01:35:04PM -0600, Benjamin Fair wrote:
On 11/25/2016 04:51 AM, David Gibson wrote:
On Wed, Nov 09, 2016 at 10:58:32AM -0600, Benjamin Fair wrote:
[...]
I like the concept of a helper to read entries from reg, but there
some things about the execution of it I think need some more thought.
Thanks for the review.
[...]
diff --git a/libfdt/fdt_addresses.c b/libfdt/fdt_addresses.c
index eff4dbc..92cbed9 100644
--- a/libfdt/fdt_addresses.c
+++ b/libfdt/fdt_addresses.c
@@ -55,6 +55,9 @@
#include "libfdt_internal.h"
+#define BYTES_PER_CELL 4
+#define BITS_PER_CELL 32
You shouldn't need these. BYTES_PER_CELL == sizeof(fdt32_t).
Of course. Thanks. I'll get rid of them.
+
int fdt_address_cells(const void *fdt, int nodeoffset)
{
const fdt32_t *ac;
@@ -94,3 +97,62 @@ int fdt_size_cells(const void *fdt, int nodeoffset)
return val;
}
+
+static uint64_t _fdt_read_cells(const fdt32_t *cells, int n)
This is a reasonable helper, but the name is bad. "read_cells"
suggests it can read some arbitrary number of cells, but in fact all
it can do is read a 32-bit int or a 64-bit int. Plus everything is
made up of cells, but more specifically what you're doing here is
interpreting several cells as an integer in the usual encoding.
Would "cells_to_integer" be a better name? Or would you recommend something
else for this?
cells_to_integer would be ok. Or just fdt_read_integer().
Thanks for the suggestion. I changed it to fdt_read_integer()
+{
+ int i;
+ uint64_t res;
+
+ /* TODO: Support values larger than 2 cells */
I don't really see any way you could support >2 cells without
completely changing the interface.
True. I wanted to have the result be a 128 bit integer, but couldn't find a
portable way to do so. Is there a better way to go about this? Or is it fine
to only support at most 2 cells, even though the rest of libfdt supports 4?
I think just supporting 2 cells is ok - it's useful in enough
practical cases. However, I'd suggest thinking of this in a more
layered way.
First, create a helper which just locates the relevant pieces of reg
entries, returning addresses and sizes as (fdt32_t *). That's at
least somewhat useful for the >2 cells case, even though you have to
then parse the address/size yourself. In the most common case for
this, PCI (address-cells == 3), you probably want to do that anyway.
This may also be useful for cases which are <= 2 cells, but the
encoding of the address is not just a plain integer.
You can then polish up fdt_read_integer() a bit and export it.
Finally you can add another helper which combines these to directly
get you the addr+size as u64 for buses where that's suitable. Make
sure to return an error if #a or #s > 2, of course.
That seems like a good idea. I implemented this for the next revision.
+ if (n > 2)
+ return -FDT_ERR_BADNCELLS;
+
+ res = 0;
+ for (i = 0; i < n; i++) {
+ res <<= BITS_PER_CELL;
+ res |= fdt32_to_cpu(cells[i]);
+ }
+
+ return res;
+}
+
+int fdt_simple_addr_size(const void *fdt, int nodeoffset, int idx,
+ uintptr_t *addr, size_t *size)
+{
+ int parent;
+ int ac, sc, reg_stride;
+ int res;
+ const fdt32_t *reg;
+
+ reg = fdt_getprop(fdt, nodeoffset, "reg", &res);
+ if (res < 0)
+ return res;
+
+ parent = fdt_parent_offset(fdt, nodeoffset);
+ if (parent < 0)
+ return res;
So, fdt_parent_offset() is very expensive, I wouldn't recommend it in
a function that's likely to be called a lot like this. Instead I'd
suggest a function which takes the parent offset as a parameter, and
optionally a wrapper that uses fdt_parent_offset().
Great idea, I'll do this in the next revision once we have a solution for
the rest of the comments.
Would it be OK to pass in the number of address cells and number of
size cells directly instead of the parent offset?
I was thinking about this in order to minimize repeated work. Plus,
the calling function needs to know this information in order to
interpret the results anyway.
+
+ ac = fdt_address_cells(fdt, parent);
+ if (ac < 0)
+ return ac;
+
+ sc = fdt_size_cells(fdt, parent);
+ if (sc < 0)
+ return sc;
+
+ reg_stride = ac + sc;
+ /*
+ * res is the number of bytes read and must be an even multiple of the
+ * sum of ac and sc.
+ */
+ if ((res % (reg_stride * BYTES_PER_CELL)) != 0)
+ return -FDT_ERR_BADVALUE;
+
+ if (addr)
+ *addr = (uintptr_t) _fdt_read_cells(®[reg_stride * idx], ac);
I don't think uintptr_t makes sense here. The addresses in the device
tree are in whatever bus they're in, and there are a whole stack of
reasons that could be unrelated to the pointer size of environment
libfdt is running in:
- The device may be on a subordinate bus whose addresses need
to be translated
- Even at the top-level, the reg properties represent
*physical* addresses, which may not be the same as virtual
addresses in code running on the system
- libfdt may be running on a completely different system from the
one the device tree in question is aimed at (bootloaders are
only one use case for libfdt).
+ if (size)
+ *size = (size_t) _fdt_read_cells(®[ac + reg_stride * idx],
+ sc);
Likewise size_t isn't necessarily right here, although I suspect it's
less likely to break in practice.
Hmm... Is it fine to use uint64_t for both of these instead then?
Yes, I think that's reasonable. Or you could even use unsigned long
or unsigned long long - as long as you error whenever #cells is too
big for the size of that type. uint64_t is probably clearer and more
consistent, though.
Thanks, I changed it to use uint64_t
--
Benjamin Fair
--
To unsubscribe from this list: send the line "unsubscribe devicetree-compiler" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
